Composite Structural Components Research Articles

Active Thermography for Automated Testing of Composite Structural Components

Active Thermography for Automated Testing of Composite Structural Components

POSSIBILITIES OF MODELING OF COMPOSITIONS OF ALLOYS Fe-Ni-Co AIMING TO FORECAST THE PHASE TRANSFORMATIONS

In the paper the possibility of use of computational modeling for prediction of processes of phase transformation by example of small series of Fe-Ni-Co alloys has been shown. Due to complexity of structure for-mation processes in these alloys the relation between modeling and experimental work was described. Modeling allows to predict basic transformations in alloys, but it doesn`t display the real composition of structural components.

Interfacial delamination in glass-fiber/polymer-foam-core sandwich composites using singlemode–multimode–singlemode optical fiber sensors: Identification based on experimental investigation

Identification of interfacial delamination in the glass fiber/polymer-foam-core sandwich composites is difficult if the delamination does not propagate to the side surface of the specimen. However, these damages may eventually lead to compromising the sandwich composite structural component. A cost-effective novel embedded fiber optic sensor is being proposed in this manuscript, which works on the principle of multimode interference, to perform distributed sensing of interfacial delamination within the sandwich composites while in service. Even though this easy to use methodology has been used to identify interfacial delamination, this methodology can also be used for different other types of interfacial/interlaminar distributed strain sensing of samples under mechanical as well as thermal loads.

Damage detection on composite structures with standing wave excitation and wavenumber analysis

This paper describes the use of wavenumber filtering for damage detection with a signal-frequency standing wave excitation on composite structures. Using a single, fixed frequency excitation from a mounted piezoelectric transducer, the full steady-state wavefield could be obtained using a Laser Doppler Vibrometer with a mirror-tilting device. After completing the scanning, a wavenumber filtering is applied to determine dominant wavenumber components of the measured wavefield, which could be used for indicative of structural damage. Mapping processes based on local wavenumber filtering is then carried out for damaged area visualization. Also introduced are the comparison of two methods for damage identification and visualization: the local wavenumber mapping and acoustic wavenumber spectroscopy. To demonstrate the proposed techniques, several experiments are performed on composite structures with different types of damage, including debonding and delamination on composite plates. The results demonstrate that the techniques are very effective in localizing damage with the potential for the quick inspection of a variety of composite structural components.

Modelling of Continuous Damage in Composite Structural Components

Modelling of Continuous Damage in Composite Structural Components

Estudo da influência do condicionamento higrotérmico nas propriedades viscoelásticas de compósitos termoplásticos

Resumo O contínuo crescimento na utilização de compósitos termoplásticos em componentes estruturais na indústria aeroespacial deve-se, primordialmente, à flexibilidade de projeto, excelência de suas propriedades mecânicas e baixa massa específica, aliadas aos elevados valores de resistência mecânica e rigidez e baixa incidência de corrosão. No entanto, componentes que requerem exigências estruturais, quando expostos a ambientes agressivos como elevada temperatura e umidade, podem ter suas propriedades mecânicas sensibilizadas por esses fatores ambientais, e devem ser cuidadosamente avaliados antes de serem colocados em serviço. Embora existam diversos trabalhos na literatura reportando este problema para compósitos estruturais, poucos estudos relacionam, de maneira sistemática, a avaliação da absorção de umidade com o comportamento viscoelástico de matrizes de PPS reforçadas com fibras de carbono, quando este compósito é utilizado em aplicações aeronáuticas. Sendo assim, o objetivo deste trabalho é avaliar a influência do condicionamento higrotérmico nas propriedades viscoelásticas de laminados PPS/fibras de carbono. Os resultados mostram que os laminados condicionados em câmara higrotérmica apresentaram absorção de umidade segundo as leis de Fick, porém, não foram observadas variações significativas na temperatura de transição vítrea quando comparado compósitos condicionados e não condicionados.

Introducing a Novel Manufacturing Process for Automotive Structural/Semi Structural Composite Components

Potential uses of composite materials are currently being investigated by the automotive industry to reduce vehicle weight and CO2 emissions. Existing composite production processes are however, low volume and high cost. The aim of the present study was to develop a novel end-to-end production process to produce a light weight, cost effective polymer composite with reduced TAKT time and potential for structural applications. Components were produced from discontinuous random fibres mixed with an epoxy resin system. Static and dynamic mechanical testing as well as durability tests are in progress to evaluate the performance of these materials. Initial results were compared to Sheet Moulding Compound (SMC) as the benchmark composite material.

A novel methodology for the assessment of the residual elastic properties in damaged composite components

In the last decades, the use of composite materials for structural components is rapidly increasing. However, damage complexity still represents the main limitation in the further diffusion of structural composites. In this paper, an innovative non-destructive methodology for assessing the amount of damage in composite materials is proposed. The macro energetic variable Damage Index is exploited for the prediction of the local residual elastic properties in damaged composites for automotive applications. A strict correlation is found between the predicted and the actual residual elastic properties of the investigated plates. The methodology could thus represent an effective way for guiding the maintenance strategy in structural composite components subjected to damage during service.

ANSYS-based algorithms for a simulation of pultrusion processes

ABSTRACTPultrusion is a continuous and cost-effective process for a production of composite structural components with a constant cross-sectional area. To provide better understanding of the pultrusion processes, to support the pultrusion tooling design and process control, as well as to increase a reliability of the simulation results, two alternative finite element modeling approaches using the same continuous model with lumped material properties for the cured composite are developed, compared, and discussed. Each of them is constructed using the general-purpose finite element software ANSYS that results in considerable savings in development time and costs, and also makes available various modeling features of the finite element package. The first procedure is developed in ANSYS Mechanical environment and is based on the mixed time integration scheme and nodal control volumes method to decouple the coupled energy and species equations. The second procedure is performed using ANSYS CFX software with the cure reaction introduced as an additional variable. To demonstrate advantages and disadvantages of the developed procedures as well as to show their accuracy and reliability for the thermo-chemical simulation of pultrusion processes, two- and three-dimensional problems have been successfully analyzed.

Micro/macro-mechanical analysis of the interface of composite structures by a differential quadrature hierarchical finite element method

The interface of composite structures is usually modeled by assuming displacement continuous. However, the reality is that the interface is another type of material with different elastic constants and is generally of different scale compared with the matrix of the composites. This work uses a differential quadrature hierarchical finite element method (DQHFEM) to analyze the interface of composite structures. The DQHFEM allows a great number of nodes on the boundary of elements but only a few nodes inside the elements, or the reverse. Therefore, the method is very convenient for the two scale analysis of the problem. Interfaces of two types of materials are analyzed in this work: (1) the interaction of grains and grain boundaries of metals that are composites in microscale and (2) the interface of nanoparticles and the matrix of nanoparticle composites. The elastic constants of the components of composite structures are obtained from test results or by molecular dynamic simulations. Numerical analysis of the two types of composite structures shown that the DQHFEM is of high accuracy and efficiency and is suitable for two-scale analysis.

Digitally focused array ultrasonic testing technique for carbon fiber composite structures

Composite fiber reinforced polymers are highly promising structures. At present, they are widely used in different areas such as aeronautics and nuclear industries. There is a great number of advantages of composite structures such as design flexibility, low cost per cubic inch, resistance to corrosion, lower material costs, lighter weight and improved productivity. However, composites degradation may be caused by different mechanisms such as overload, impact, overheating, creep and fatigue. Comparing to inspection of other materials some unique consideration is required for testing and analysis. Ultrasound testing is the most common method for inspection of composite structures. Digitally Focused Array Technology is considered as novel approach which enables fast and effective quantitative automatic testing. In this study new methodology of quality assurance of composite structure components based on DFA is performed.

Failure mechanism based modelling of impact on fabric reinforced composite laminates based on shell elements

A shell element based modelling strategy for simulating impact on fabric reinforced laminated composites within the framework of the Finite Element Method is presented. Thereby, each ply of the laminate is represented by its own layer of shell elements. The interfaces in-between are discretised by cohesive zone elements. Material nonlinearities within plies, i.e. fibre rupture, matrix cracking and plasticity-like effects, and interfaces, i.e. delamination, are accounted for by appropriate constitutive laws. Impact simulations of a rectangular laminated composite plate with quasi-isotropic layup in a drop tower test setup are conducted. The predictions are based on material parameters partly from corresponding material data sheets and partly estimated from the literature. Thus, no inverse model calibration is applied. The acquired simulation results are validated with accompanying experiments. The predicted spatial distribution of ply damage and delaminations, as well as the associated energy absorption agree very well with the experimental results. The approach shows excellent performance in terms of computational efficiency such that simulations of the impact behaviour of structural composite components become feasible.

Improvement of toughness and shear properties of multiwalled carbon nanotubes/epoxy composites

In this work, Epocast 50‐A1/946 epoxy have been modified with different weight percentages (0.25, 0.5, 0.75, 0.1, 1.25, and 1.5 wt%) of multiwalled carbon nanotubes (MWCNTs). Because of Epocast epoxy was primarily developed for joining and repairing of composite aircraft structural components, the optimum weight percentage of MWCNTs must be determined based on trade‐offs between the optimum tensile, in‐plane shear and toughness properties of the developed MWCNTs‐composites, which is the objective of this study. The effect of MWCNTs on the toughness and in‐plane shear was studied using single‐edge notch tension and Iosipescu shear tests, respectively. The experimental results showed that the composite materials with 0.75 wt% MWCNTs has the highest improvement in the in‐plane shear properties compared to the neat epoxy. While the maximum improvements in the tensile and toughness properties were observed at 0.5 wt% MWCNTs. Eleven models were selected from an extensive literature survey, for predicting the in‐plane shear moduli of the developed MWCNTs‐composites. The modified rule of mixture can effectively predict the in‐plane shear moduli of the composites with MWCNTs up to 0.75 wt%. While the nonlinear behavior of the modified Halpin–Tsai model with exponential shape function is the closest to the experimental results up to 1.5 wt% MWCNTs. POLYM. COMPOS., 39:815–825, 2018. © 2016 Society of Plastics Engineers

Axial deformability of the composite lattice cylindrical shell under compressive loading: Application to a load-carrying spacecraft tubular body

Analysis of axial deformability of filament-wound composite anisogrid lattice tubular body of the spacecraft subjected to compressive loading is presented in the paper. The axial compressive load is applied to the lattice cylinder through the rigid ring attached to its end. The lattice structure is modelled using a continuum model of the orthotropic cylindrical shell. Based on this model, an analytical formula providing the value of the axial deformation of the rigid ring and assessment of the shell’s axial stiffness is derived. This formula is verified by the finite-element analysis and employed to investigate the effects of the length, number of helical ribs and their angle of orientation on the axial deformability of the lattice cylinder. Using these results the full size physical prototype of the spacecraft body was designed, manufactured and tested. The axial displacement predicted by the analytical formula is correlated well with that measured in the experiment. Thus, the analytical formula proposed in this work can be utilised by design engineers in the efficient design analyses of similar composite lattice structural components.

Explicit Finite Element Modelling as a Development Tool for New Ultrasound Testing Methodologies for Detection and Characterization of Porosity and Defects in Composites

Abstract Composite components frequently contain porosity or defects, which might, in some circumstances, be deemed benign. Other defects could lead to progressive or sudden failure in service; hence reliable and accurate material condition monitoring and health assessment is an important prerequisite for further design for the use of composite materials in high duty and life sensitive engineering components. The objective of this paper was to demonstrate the use of explicit finite element as an effective development tool in the development of ultrasound testing methodologies for the characterization of porosity in composites – a virtual ultrasound vibration laboratory. This would enable an improved inspection sentencing capability for as-manufactured composite structural components. It would also be of benefit in sentencing components subject to foreign object damage (FOD) in order to determine whether the component can continue in service, possibly with in-service monitoring or cosmetic repair, or must be condemned. In this work, finite element models simulating damage and porosity were presented. The models were compared with ultrasound tests on real specimens with practically relevant defects. Experimental tests, making use of wave superposition from two piezo-electric vibration sources, were shown to detect energy absorbing damage in the specimen, such as might have been created by impact or crush loads. The same piezo-electric vibration system was also used to measure the dissipated energy. Computational analysis, using simple material model variations, was able to replicate the Lamb wave generation and evolve a wave form resembling a “standing wave.” The computational material model was modified to represent porosity in composites.

The Influence of the Thickness of a Rebar on the Growth Kinetics and Structure of Hot Dip Zinc Coatings

In the paper the results of tests on obtaining zinc coatings on reinforcing steel are presented. The coatings were obtained in a zinc bath on B500SP rebars of various diameters. The structure of coatings obtained on rebars with the diameter of 12, 16, 20 and 32 mm has been developed. The chemical composition of structural components of the coating has been established. The growth kinetics of coatings obtained in the traditional galvanizing process at the temperature of 450°C has been established and the impact of the rebar diameter upon the coating growth curve has been defined. The obtained coatings are continuous and they are quite thick. Moreover, it has been determined that an increase in the rebar thickness induces an increase in the coating thickness.

Damage detection tomography based on guided waves in composite structures using a distributed sensor network

Structural health monitoring (SHM) based on guided waves allows assessing the health of a structure due to the sensitivity to the occurrence of delamination. However, wave propagation presents several complexities for effective damage identification in composite structures. An efficient implementation of a guided wave-based SHM system requires an accurate analysis of collected data to obtain a useful detection. This paper is concerned with the identification of small emerging delaminations in composite structural components using a sparse array of surface ultrasonic transducers. An ultrasonic-guided wave tomography technique focused on impact damage detection in composite plate-like structures is presented. A statistical damage index approach is adopted to interpret the recorded signals, and a subsequent graphic interpolation is implemented to reconstruct the damage appearance. Experimental tests carried out on a typical composite structure demonstrated the effectiveness of the developed technique with the aim to investigate the presence and location of damage using simple imaging reports and a limited number of measurements. A traditional ultrasonic inspection (C-scan) is used to assess the methodology.

Trace-based stiffness for a universal design of carbon-fiber reinforced composite structures

A novel invariant-based approach to describe stiffness and strength of carbon-fiber reinforced plastic (CFRP) composites has recently been proposed in the literature. The approach is based on the trace of the plane stress stiffness matrix as a material property. The proposed method allows predicting strength and stiffness of the CFRP composite laminates within 1.5% error using [0] ply test only. The current study evaluates the use of the trace-based approach to set up a universal stress–strain relation among various materials and orthotropic laminates for composite structural components. One such stress–strain relation was evaluated for many CFRP composites using a beam subjected to in-plane and flexural loads. The current approach using the trace was found to be simple and accurate in the optimal design of composite structures once a geometric profile is defined by an isotropic material such as aluminum. Weight savings of composite laminates and structural components with various material and orthotropy combinations over aluminum can simply be determined with the current approach.

Experimental Investigation on Buckling Analysis of Woven Glass Fiber/Epoxy Laminated Composite Materials

The structural components made from the composite materials possess outstanding advantages like reliable mechanical properties, durability, and good corrosion resistance, and low density. They also exhibit high impact resistance and good damage tolerance. These merits of composite structures draw the attention of scientists, engineers and researchers in generally the stability of composite structures is verified by carrying out buckling analysis. The aircraft components are made up of laminated composite plates are subjected to buckling analysis, in order to confirm whether the component withstand the critical in plane loads. Composite structural plates provided with circular cut out, square cut out and rectangular cut-out are widely used as structural members in aircraft and vehicle design. The different holes are provided in these members can be access holes, pass-through holes for any hardware or holes for windows and doors. Sometimes these holes are produced for weight reduction in the composite structural components. In this present study, buckling experiments were carried out on Epoxy/woven glass fiber laminated composite plate specimens and the influence of different cut-out shapes like circular, square and rectangle are examined and determined experimentally. Boundary conditions free and clamped were considered for all the experiments. After the buckling experiments, comparisons were made between these two test results. These results show the effect of various cut-out shapes on the buckling load.

Design and Development of Constant Stress Composite Cantilever Beam

Composite materials, due to their unique properties such as high strength to weight ratio, corrosion resistance, and impact resistance have huge potential as structural materials in automotive, construction and transportation applications. However, these properties often come at higher cost owing to complex design methods, difficult manufacturing processes and raw material cost. Traditionally, tapered laminated composite structures are manufactured using autoclave manufacturing process by ply drop off technique. Autoclave manufacturing though very powerful suffers from high capital investment and higher energy consumption. As per the current trends in composite manufacturing, Out of Autoclave (OoA) processes are looked as emerging technologies for manufacturing the structural composite components for aerospace and defense applications. However, there is a need for improvement among these processes to make them reliable and consistent. In this paper, feasibility of using out of autoclave process to manufacture the variable thickness cantilever beam is discussed. The minimum weight design for the composite beam is obtained using constant stress beam concept by tailoring the thickness of the beam. Ply drop off techniques was used to fabricate the variable thickness beam from glass/epoxy prepregs. Experiments were conducted to measure bending stresses along the span of the cantilever beam at different intervals by applying the concentrated load at the free end. Experimental results showed that the stresses in the bean at different intervals were constant. This proves the ability of OoA process to manufacture the constant stress beam. Finite element model for the constant stress beam was developed using commercial finite element simulation software. It was observed that the simulation results agreed very well with the experimental results and thus validated design and manufacturing approach used. Keywords—Beams, Composites, Constant Stress, Structures.